Polymer blends can be formed or shaped into lightweight and durable articles useful, for example, as automobile parts, toys, and housings for various types of equipment. Unfortunately, polymer blends such as those formed of polyethylene, polypropylene and rubber are difficult to treat so that the paint durably adheres to the surface of the article. Paint adhesion is a particular concern in the case of blends derived from thermoplastic olefin ("TPO") compositions such as those disclosed U.S. Pat. Nos. 4,480,065; 4,412,016 and 4,439,573.
TPO compositions are blends of synthetic rubber and polyolefins such as polypropylene and polyethylene. Because articles made from TPO compositions have gained acceptance in the automotive industry as body parts and the like, it is important that paint sufficiently adheres to the TPO composition to withstand petroleum fluids such as gasolines and the like.
Articles formed of TPO blends which contain substantial amounts of polypropylene exhibit poor adherence for coating paints. These compositions therefore must be treated prior to applying coating materials such as paints by the application of interlayer coatings to promote adhesion. Unfortunately, articles made from TPO compositions are difficult to treat so that the paint adheres against the action of petroleum fluids such as gasolines which dissolve the interlayer coatings. Many paints either do not adhere to the TPO composition, or peel or chip away under normal use, high humidity conditions, or in the presence of fuels or solvents.
Various methods have been tried to improve the adherence of TPO compositions having substantial amounts of polypropylene and/or rubber for paints. Methods of the art have employed primers or adhesion promoters such as chlorinated polyolefins, as well as surface treatments. Although these methods have improved the adherence of these compositions for coating materials such as paints, these methods have not been entirely satisfactory. For example, adhesion promoters such as chlorinated olefins are suspectable to attack by petroleum fluids such as gasolines. Also, the prior art methods for increasing adherence of polymer compositions are costly and time consuming.
A need therefore exists for polymer compositions that show improved adherence for coatings such as paints to enable manufacture of coated polymer compositions which show improved resistance to attack by fluids.